The present invention relates to lubricating grease compositions and the preparation thereof and more especially with lubricating greases having low noise characteristics.
Industrial lubricating greases are homogeneous products of a semi-liquid to solid consistency. Essentially they consist of a dispersion of a thickener in a liquid lubricant or base oil. In general the thickener is a significant determinant of the properties of the greases.
Typical thickeners used in forming greases include metal soaps, such as lithium salts of fatty acids, non-soaps such as organophilic clay minerals and polyurea compounds.
To improve the performance properties of a grease additional materials may be incorporated in the base grease, such as extreme pressure additives, antioxidants, rust-inhibitors, viscosity index improvers and mixtures thereof.
In preparing grease compositions a thickener and the other additives often are added to the base oil and the resulting mixture is heated and stirred and then passed through a roll mill or the like to obtain the grease. In the case of polyurea thickened greases the polyurea generally is prepared in situ by the reaction of amines with isocyanates in a base oil, followed by mixing with the other additives and milling to provide a homogeneous end grease composition.
User demand for low noise greases in bearing applications has been increasing steadily; however, manufacturing greases with low noise characteristics has proven time consuming and expensive compared to more conventional greases.
Accordingly an object of the present invention is to provide an improved process for making a grease with low noise characteristics which is less time consuming.
Another object of the present invention is to provide a process for making a grease which can be practiced on an industrial scale.
These and other objects of the invention will become apparent upon from the following description of the invention.
Simply stated, a grease composition having low noise characteristics is prepared by:
shearing a mixture of a base oil and thickener for a time sufficient to reduce substantially all of thickener particles sizes below 500 microns; and
processing the sheared mixture to a grease.